1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, a semiconductor device having a MIM (Metal-Insulator-Metal) type capacitor made of a high dielectric constant film and a method of manufacturing the same.
2. Description of the Prior Art
In the semiconductor memory device having a capacitor such as DRAM (Dynamic Random Access Memory), miniaturization of the capacitor is desired as the integration density of the device is increased higher. Therefore, material with a high dielectric constant, e.g., tantalum oxide (Ta2O5), etc. is recently employed as a capacitor insulating film.
The capacitor consists of a lower electrode, a dielectric film (capacitor insulating film), and an upper electrode. As the capacitor structure, a plate type structure as well as a cylinder type structure which is excellent in the integration density is employed. The plate type capacitor has been disclosed in Patent Application Publication (KOKAI) Hei 2-226754, Patent Application Publication (KOKAI) Hei 6-275776, Patent Application Publication (KOKAI) Hei 3-136361, and Patent Application Publication (KOKAI) Hei 8-139288, for example.
As disclosed in Patent Application Publication (KOKAI) Hei 2-226754 and Patent Application Publication (KOKAI) Hei 6-275776, the lower electrode of the capacitor is connected to the impurity diffusion region on the semiconductor substrate. Therefore, if the impurity diffusion region is formed shallow, the lower electrode is often formed by a silicon film which is the same material as the semiconductor substrate. In case the cylinder type capacitor is employed, tungsten (W) is not suitable for constituent material of the lower electrode if easiness in working needed to form the lower electrode into the cylindrical shape is taken into consideration. Thus, in most cases polysilicon is employed as the constituent material of the lower electrode.
Further, if a tantalum oxide film is employed as the capacitor insulating film, a method of re-oxidizing the tantalum oxide film by annealing is employed to improve the film quality of the tantalum oxide film. In this case, if the polysilicon film is used as the lower electrode, it is possible that the polysilicon film reacts with the tantalum oxide film in above annealing to thus increase a leakage current into the impurity diffusion layer. It is also possible that, since a natural oxide film with a low dielectric constant is formed on a surface of the polysilicon film, reduction in capacitance is caused.
In Patent Application Publication (KOKAI) Hei 2-226754, in order to prevent increase in the leakage current and reduction in the capacitance, a tungsten oxide (WO2) film which has a high dielectric constant is employed as the capacitor insulating film which is in contact with the lower electrode. In this case, a tungsten film is employed as the upper electrode.
In Patent Application Publication (KOKAI) Hei 6-275776, in order to prevent the leakage current, a tungsten nitride (WN) film is employed as the upper electrode which is in contact with the tantalum oxide film. In this case, the polysilicon film is employed as the lower electrode and also a silicon oxide film is interposed between the polysilicon film and the tantalum oxide film.
In Patent Application Publication (KOKAI) Hei 3-136361, the tungsten film is employed as both the lower electrode and the upper electrode. In this case, in order to prevent reaction between the silicon constituting the semiconductor substrate and the tungsten film constituting the lower electrode, the tungsten nitride is interposed between the lower electrode and the semiconductor substrate.
In Patent Application Publication (KOKAI) Hei 8-139288, there are such descriptions that amorphous silicon is employed as the lower electrode, then the tungsten film and the tantalum oxide dielectric film are formed on the lower electrode, and then the upper electrode made of the titanium nitride is formed on the tantalum oxide dielectric film to thus form the capacitor. In this case, in selective growth of the tungsten film, such a step is contained that a reduction gas such as a silane (SiH4) gas in addition to a tungsten halogenated gas is employed together.
However, as set forth in Patent Application Publication (KOKAI) Hei 2-226754, in case the tungsten oxide film is interposed between the polysilicon film and the tantalum oxide film, there has been a possibility that the leakage current passing through an interface between the tantalum oxide film and the polysilicon film is increased.
Also, as set forth in Patent Application Publication (KOKAI) Hei 6-275776, the silicon oxide film is interposed between the lower electrode made of polysilicon and the tantalum oxide film, which causes reduction in the capacitance as a whole capacitor.
In addition, if oxygen in the tantalum oxide film is diffused into the polysilicon of the lower electrode via the silicon oxide film, the tantalum oxide film is deteriorated, or silicon in the silicon oxide film or the polysilicon film reacts with the tantalum oxide film to thus cause the increase in the leakage current.
Also, as set forth in Patent Application Publication (KOKAI) Hei 3-136361, it is not suitable for the capacitor which has a complicated shape such as the cylinder type capacitor, to form the lower electrode and the upper electrode by the tungsten film.
Also, as set forth in Patent Application Publication (KOKAI) Hei 8-139288, in case the tungsten film, the tantalum oxide dielectric film, and the tantalum nitride film are formed on the lower electrode made of silicon to construct the capacitor, the tungsten film is silicided by annealing process if annealing process such as annealing process to improve the crystal property of the tantalum oxide dielectric film, thermal nitriding process of tantalum, or the like is applied at 500xc2x0 C. or more. Then, after the tungsten film has been silicided, silicon in the tungsten film reacts with oxygen contained in the tantalum oxide dielectric film, so that silicon oxide (SiO2) is formed between the tantalum oxide dielectric film and the tungsten film. As a result, since the silicon oxide has a lower dielectric constant than the tantalum oxide, the capacitance of the capacitor is reduced.
It may be thought about that, in order to prevent generation of such silicon oxide, the temperature of the annealing process is set lower than 500xc2x0 C. The crystal property of the tantalum oxide dielectric film cannot be sufficiently improved to such extent that the leakage current in the capacitor can be suppressed satisfactorily.
It is an object of the present invention to provide a semiconductor device capable of preventing reaction between upper and lower electrodes and a tantalum oxide film, and also preventing diffusion of oxygen contained in a dielectric oxide film into the upper and lower electrodes, and a method of manufacturing the same.
The above object can be overcome by providing a method of manufacturing a semiconductor device comprising the steps of forming a semiconductor film connected to a semiconductor substrate; forming a capacitor lower electrode made of a tungsten film selectively on a surface of the semiconductor film by causing a tungsten compound gas to react with the semiconductor film; forming a tungsten nitride film by nitriding a surface of the tungsten film by using a nitrogen gas or a nitrogen containing gas; forming a capacitor dielectric film made of oxygen compound on the tungsten nitride film; annealing the capacitor dielectric film in a n oxygen containing gas; and forming a capacitor upper electrode made of a conductive film on the capacitor dielectric film.
Also, the above object can be overcome by providing a semiconductor device comprising impurity diffusion regions formed on a semiconductor substrate; an insulating film formed on the semiconductor substrate and having opening portions on the impurity diffusion regions; a capacitor lower electrode formed on the insulating film and made of a semiconductor film containing impurity connected to the impurity diffusion regions via the opening portions; a tungsten film of the capacitor lower electrode, formed on the semiconductor film; a tungsten nitride film of the capacitor lower electrode formed on the tungsten film; a capacitor insulating film containing oxygen, formed on the tungsten nitride film; and a capacitor upper electrode made of a conductive film being formed on the capacitor insulating film.
In the present invention, the tungsten nitride film is formed as the conductive film of the lower electrode which is contact with the capacitor dielectric film containing the oxygen.
As the method of forming the tungsten nitride film, such a method is adopted that the tungsten film is formed by causing the tungsten containing gas to react with the semiconductor and then the tungsten film is exposed to nitrogen.
When the capacitor dielectric film is processed by heating after the capacitor dielectric film containing the oxygen has been formed on the lower electrode, such tungsten nitride film can function as a barrier layer against the oxygen. For this reason, since diffusion of the oxygen from the capacitor dielectric film, e.g., tantalum oxide film to its peripheral portion can be suppressed, an amount of oxygen in the tantalum oxide film can be assured and therefore the film quality can be maintained.
Since the semiconductor film is employed as the basic portion of the lower electrode of the capacitor, the complicated structure capacitor like the cylinder type can be relatively easily formed as the capacitor.
As a result, the capacitor with the complicated structure can be formed, and also the leakage current of the capacitor can be suppressed as a whole.
The above object can be overcome by providing a method of manufacturing a semiconductor device comprising the steps of forming a semiconductor film made of silicon or silicon compound, into which impurity is doped, to be connected to a semiconductor substrate; forming a refractory metal film selectively on a surface of the semiconductor film in an atmosphere not-containing a reduction gas by introducing a refractory metal halogenated gas into the atmosphere; forming a refractory metal nitride film by nitriding a surface of the refractory metal film; forming a dielectric oxide film of group elements, group elements, or group elements on the refractory metal nitride film; and crystallizing the dielectric oxide film by virtue of heat treatment at 500xc2x0 C. or more. In the method of manufacturing the above semiconductor device, an impurity concentration in the semiconductor film is set to more than 1.5xc3x971017 atoms/cm3.
In the present invention, in case the refractory metal film is formed on the semiconductor film made of silicon which contains the impurity, the refractory metal halogenated gas is employed in the atmosphere which does not contain the reduction gas such as the silicon compound gas. The refractory metal film being formed by such method becomes difficult to react with constituent elements of the semiconductor film, so that the compound of the semiconductor and the refractory metal film is not generated. The impurity concentration of the semiconductor film is set to more than 1.5xc3x971017 atoms/cm3.
Accordingly, since semiconductor elements are not contained in the refractory metal nitride film being obtained by nitriding the refractory metal film, the semiconductor oxide film, e.g., silicon oxide having a low dielectric constant can be prevented from being formed between the refractory metal nitride film and the dielectric oxide film even when the refractory metal nitride film is heated at 500xc2x0 C. in forming the dielectric oxide film on the refractory metal nitride film or succeeding steps.
Accordingly, reduction in the dielectric constant between the upper electrode and the lower electrode can be prevented, so that reduction in the capacitance of the capacitor can be prevented.
In the structure other than the capacitor, when the refractory metal film and the refractory nitride film are formed between the silicon film and the metal film, such refractory metal film can be utilized as the barrier metal of oxygen.